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Changing brake fluid can be a slippery subject. Some manufacturers include it in their maintenance schedules and others don't.
Mercedes-Benz, for example, says brake fluid should be replaced every two years or 20,000 miles, and Volkswagen says that should be done on most of its models every two years regardless of mileage. Subaru recommends fresh brake fluid every 30,000 miles.
On the other hand, most Chevrolets can go 150,000 miles or 10 years, according to Chevy's maintenance schedule, and many Ford, Chrysler and Toyota vehicles don't list brake fluid as a regular maintenance item.
Check your car's owner's manual to see what the manufacturer recommends. You might also want to discuss the slippery subject of brake fluid with a trusted mechanic if the manufacturer doesn't give any guidance. Don't be surprised if a mechanic suggests replacing the brake fluid periodically, because mechanics probably have seen what can happen if you don't.
What can happen? Even though brake fluid dwells in a sealed system it still can absorb moisture over time, and that can lead to corrosion in the brake system. Moisture also lowers the boiling temperature of brake fluid, and that can reduce braking effectiveness in repeated hard stops.
If the manufacturer lists a 10-year interval or none at all for replacing brake fluid, how often should you have it done?
Every two or three years is probably too often, though if it helps you sleep at night, then go for it. Just be aware that some service shops, especially those that make their living by replacing fluids, might try to scare you with dire warnings that disaster is imminent unless you flush all your vehicle's fluids long before it is necessary.
Unless the manufacturer calls for it sooner, we would wait four or five years and have it done at the same time as other brake work, such as replacing pads or rotors. Replacing brake fluid is cheaper than replacing brake lines or a master cylinder that has corroded, so don't automatically dismiss the recommendation of a mechanic as just salesmanship.
And no matter who suggests fresh brake fluid, make sure they're replacing it with the type that is called for by the vehicle manufacturer. Some vehicles require DOT 3 fluid, others a different variety, such as DOT 5, so consult your owner's manual before you give the go ahead.